Here's the sugar-free sweetner ("Pal Sweet") that I use - same sweetness with sugar, but 90% low in calories with zero sugar.
Peel the sweet potatoes and chop into small chunks. Soak in water for 20 minutes.
Put that into a microwave-safe container. Cover with plastic wrap, and microwave until soft. *It's usually 7 minutes at 600 W, flip it over for another 5 minutes, then steam in the microwave for 3 minutes.
Transfer the sweet potatoes into a bowl and mash while it's hot.
Pass it through a strainer. *It's actually easier to do this after Step 6 - it's up to you.
Put the sweet potatoes and butter into a pan. Knead well. Add milk, heavy cream, PAL sweet, and salt. Cook over low heat. *60 ml milk, 30 ml heavy cream.
Let's taste. Sometimes the sweet potatoes aren't sweet enough, so increase the amount of sugar if necessary.
*You could also add some honey (unlisted) to improve the taste. In that case, use less sugar!
Mix well to remove excess moisture. When it's thick, turn the heat off. *Ideally, it shouldn't stick to your finger when touched, but it's alright if it's slightly sticky!
Leave aside to cool down slightly. Now add the egg yolk and vanilla extract. Mix well. *If you add the egg yolk immediately after removing from the heat, it will harden the batter!
Preheat oven to 180°C.
Divide the batter into your preferred sizes. Shape into an half-oval.
Mix egg yolk into water for the egg wash. Brush it onto the surface of the sweet potatoes. *Don't use it all up or throw it away - you will use it again later.
Bake for 30 minutes in 180°C oven. *After 20 minutes, take it out and brush on the egg wash again. Continue baking for another 10 minutes.
Done. It's the most delicious when freshly baked. When it's gone cold, just heat in a toaster oven. This will improve the taste and brown the tops nicely.
Also check out my recipe for "Cocoa Pudding" using sugar-free sweetener (Recipe ID: 1325707).
Story Behind this Recipe
I made my standard sweet potato treats using sugar-free sweetener.
-You've got to pass it through a strainer!! This really makes a difference to the texture!! -If the fiber of the sweet potatoes get stuck in the strainer, rinse it once to use again. -Make sure to evaporate the moisture well after adding milk into the sweet potatoes!!